1. Field of the Invention
This invention relates to a barrel plating device.
2. Description of the Related Art
In a barrel plating device that is to apply plating to works of a length as small as 0.2 to 1 mm, for instance, it is important to prevent the small works from entering each clearance (specifically, a bearing portion) between a lead wire of an electrode (specifically, a cathode) mounted to an inter-opposite end rotation center of a barrel and an insertion hole adapted to permit insertion of the lead wire, while the barrel plating device is in operation. This is because the electrode lead wire is inserted into each electrode lead wire bearing portion to ensure that the above lead wire may not rotate for the rotating barrel, so that entering of the small works into the above bearing portion causes damages to a coated insulation layer on the above lead wire and an inside face of the above insertion hole or obstruction to rotation of the barrel.
In Japanese Patent Laid-open No. 2002-256500, for instance, there is described a bearing part constitution of the barrel plating device as shown in FIG. 11.
The barrel plating device shown in FIG. 11 has a barrel holding frame 2a obtained by interconnecting a pair of support members 20a facing each other at a prescribed interval with a plurality of connecting bars. Tubular support shafts 4a are respectively mounted in a piercing form to the support members 20a with screws 44a so as to be located on the same horizontal axis.
A barrel 3a is composed of a hollow drum part (of a hexagonal prism shape, for instance) (not shown) and end plates 31a respectively fixed to the drum part so as to close the opposite ends of the drum part. A pivotally movable cover is mounted to one side surface of the drum part. The barrel drum part is a part obtained by combining, into a unit, porous plates having a large number of small holes adapted to permit permeation of a plating solution.
The opposite ends of the barrel 3a that is in an inclined position to a horizontal rotation axial center by about 11 degrees in a vertical direction are supported with the support shafts 4a in a rotatable condition. Specifically, a boss-shaped member 31b fixed to the bearing portion of each barrel end plate 31a is mounted to an oppositely facing-side end of the corresponding support shaft 4a through a super-high density polyethylene bearing 49a in a rotatable condition. In addition, an end gear 60a of a rotation transmitting means adapted to transmit rotation from a motor (not shown) to the barrel is fixed in a vertical position to one boss-shaped member 31b. 
Each tubular support shaft 4a has a hollow part 40a composed of a distal end-side large inside diameter part 40b and an oppositely facing side-end small inside diameter part 41a. A super-high density polyethylene bush 32a mounted to each barrel end plate 31a has an insertion hole 32b so as to have the same axis as an axis of the hollow part 40a of each support shaft 4a. 
An electrode lead wire 10a is inserted into the hollow part 40a of each support shaft 4a and the insertion hole 32b of each bush 32a so as to extend from the outside of the corresponding support member 20a into the barrel. In an inserted condition of each lead wire 10a as described above, an inside diameter of the above small inside diameter part 41a is sized so that an outside surface of the above lead wire 10a closely contacts, and an inside diameter of the insertion hole 32b is sized so that any work may not flow into a clearance between an inside surface of the above insertion hole 32b and the outside surface of the above lead wire 10a. 
The outside surface of each lead wire 10a is coated with an insulation layer consisting of rubber. The above lead wire 10a has a downwardly bent part at a portion inside the barrel, and an electrode (specifically, a cathode) is connected to a tip end of the downwardly bent part.
An electrode lead wire mounting structure at the other end of the barrel is the same as the mounting structure shown in FIG. 11, except that the support shaft 4a at the other end of the barrel is sized to be shorter than that shown in FIG. 11, because of no need for the end gear 60a of the rotation transmitting means shown in FIG. 11.
When the above barrel plating device is used to apply plating to works composed of a microchip capacitor having a diameter of about 0.3 mm, for instance, the barrel cover is firstly opened to inject a prescribed amount of works and dummies into the barrel. Then, the barrel cover is closed, and the barrel is set, inclusive of the barrel holding frame 2a, in a plating tank to such a degree that the barrel gets immersed in a plating bath of the plating tank. Then, rotation of the barrel is started at a low speed with the electrodes energized. After plating to the works is finished, the barrel is transferred, inclusive of the barrel holding frame, from the plating tank to a cleaning bath for cleaning the works together with the dummies. Then, the works and the dummies are subjected to drying.
The above barrel plating device has no possibility of causing any work to flow into each clearance of the bearing portion, since each electrode lead wire is mounted as described above, and the inside diameter of the small inside diameter part 41a of each support shaft 4a is sized so that the outside surface of the above lead wire 10a closely, contacts, while the inside diameter of the insertion hole 32b is sized so that any work may not flow into the clearance between the inside surface of the above insertion hole 32b and the outside surface of the above lead wire 10a. 
Thus, the above barrel plating device is supposed to be effective in preventing adverse effects caused by the fact that the works enter each clearance (such as each bearing portion clearance) between the insertion hole 31b and the lead wire 10a, specifically, adverse effects such as damages to the coated insulation layer on the above lead wire 10a, obstruction to smooth rotation of the barrel and unsatisfactory plating caused by the fact that the works remaining in the above clearance are mixed with later injected works, for instance.
However, according to the above barrel plating device, the lead wire insulation layer in the bearing portion has low molding accuracy and high coefficient of thermal expansion. Thus, when the above barrel plating device is used to apply plating to works of a length as small as 0.2 to 1 mm, for instance, it is difficult to control the inside diameter of the insertion hole 32b of the bush 32a in each barrel side plate to attain an inside diameter as much as a size, which ensures that the above works or a part thereof may not enter the clearance between the inside surface of the above insertion hole 32b and the above lead wire 10a, specifically, each bearing portion clearance, in consideration of the low molding accuracy and the coefficient of thermal expansion of the insulation layer.
Consequently, when appropriate control of the size of the insertion hole 32b of each bush 32a is not attainable so that the above insertion hole 32b remains small-sized, the above barrel plating device develops such adverse effects that the clearance between the inside surface of the above insertion hole 32b and the outside surface of the above lead wire 10a becomes larger in size due to wear of the insulation layer of the above lead wire 10a so that the works or the part thereof enters the above clearance, in addition to disadvantages of making rotation of the barrel difficult due to severe friction between the inside surface of the above insertion hole 32b and the outside surface of the above lead wire 10a when the barrel is in rotation. On the contrary, when appropriate control of the size of the insertion hole 32b is not attainable so that the above insertion hole 32b remains large-sized, the above barrel plating device also develops such adverse effects that the works or the part thereof enters the above clearance when the barrel is in rotation.
The works or the part thereof enters each clearance between the insertion hole 32b and the lead wire 10a and is stuffed in the above clearance, resulting in adverse effects such as damages to the coated insulation layer on the above lead wire 10a, non-smooth rotation of the barrel and degraded plating homogeneity caused by the fact that the works stuffed in the above clearance remain within the barrel when takeout of the works from the barrel is performed after plating.